Coating apparatuses for boards or board-shaped workpieces are known in various forms and are used especially in the coating of printed circuit boards (for example with solder resist, etc.). Such a coating apparatus and its basic method of functioning are described, for example, in EP-A-145 648. The board to be coated is passed under a pouring curtain which falls from a curtain pouring head. The pouring head is so arranged that the falling pouring curtain strikes the board along a line of impact extending transversely to the direction of transport of the board. By continuous advance of the board under the pouring curtain the board is in that manner coated.
In addition, a transport apparatus for such printed circuit boards to be coated is known from EP-A-312 498. There, the boards to be coated are first so aligned in a feed station using rake-like aligning means that, thereafter, the board edges are arranged approximately parallel to the direction of transport of the board. The board aligned in that manner is conveyed by means of first transport means, which are in this case in the form of a feed roller conveyor, to a curtain coating device of the type described above. In the curtain coating device are provided two transport means that pass the boards to be coated under the pouring curtain as soon as the entire board to be coated has entered the coating device.
The reason for the necessity for two transport means is that the boards have to be passed under the pouring curtain at a greater speed than that at which they enter the curtain coating device from the feed station. The speed at which the boards are passed under the pouring curtain depends on several factors, but especially on the type of coating composition (for example resist) and on the height from which the curtain falls. The fact that the transport speed in the curtain coating device is greater than the feed speed also ensures that there is a certain time buffer between two consecutive boards.
The apparatuses described are functionally efficient devices per se but still have disadvantages. For example, in the case of the devices described, it is necessary to align the boards in two separate operations and to transfer the aligned boards to the curtain coating device. That is first of all complicated, that is to say, two separate devices are required, on the one hand aligning means (for example the rake described above) and, on the other, means for transferring the boards to the second transport means. Secondly, such means also require a certain mount of space which, in an age of progressive size reduction, is in increasingly short supply (and expensive besides).
Other disadvantages of already existing devices reside also in the fact that the boards in the curtain coating device lie on conveyor belts and, resting on those belts, are transported through the pouring curtain, as a result of which the quality of the contact face may be impaired. Problems may therefore arise during transport of the board through the curtain because the conveyor belts, on both sides of the curtain, extend only to just short of the curtain so that the falling curtain cannot fall on the conveyor belts during the coating operation. If the board to be coated is not quite flat, problems may arise as the board passes from the one belt, which extends to just upstream of the curtain, onto the belt that begins just downstream of the curtain, because the board is not flat. Furthermore, the conveyor belts can still be soiled comparatively easily, for example, when the leading board edge breaks through the pouring curtain and coating composition is "pushed" by the edge onto the conveyor belt or passes onto the conveyor belt through drill-holes in a blank.